1. Field of the Invention
The present invention relates to a time division multiple access (TDMA) voice information reading apparatus for reading out voice data from data received by TDMA and, more particularly, to a TDMA voice information reading apparatus which delays voice data until synchronous detection even upon receipt of out of frame reception data (e.g., a pull-out of reception data) in a transmission line such as a radio channel, thereby normally reading out the voice data and outputting it.
2. Description of the Prior Art
Conventionally, a TDMA voice information reading apparatus of this type is applied to, e.g., a portable telephone. In this case, the timing of reception data sometimes shifts from the original timing due to the distance from a cell base station connected via a radio channel or multiple radio wave propagation (multipath) at an obstacle at the moving position. That is, voice data out of phase may be received.
A xe2x80x9cbit synchronization circuitxe2x80x9d disclosed in Japanese Unexamined Patent Publication No. 4-10725 is known as a measure against such reception data out of phase. In this prior art, when a pull-out occurs, erroneous data is not read out from the FIFO memory. That is, the data out of phase is discarded.
FIG. 1 is a block diagram showing the arrangement of main part (TCH (Traffic Channel) read circuit) of a conventional TDMA voice information reading apparatus. Referring to FIG. 1, the TCH read circuit has a TCH data read window generation circuit 13 for generating TCH data read window data S1 of high level at a free-running timing. The TCH read circuit also has an AND gate 12 for receiving the TCH data read window data Si and reception data S2 and outputting voice output data S14 to a digital signal processor (DSP) (not shown) for processing speech communication voice data, and a synchronous detection circuit 5 for detecting synchronization from the reception data S2 and sending bit shift data S8 representing the shift of the reception data S2 from the prescribed timing to the TCH data read window generation circuit 13.
FIGS. 2A to 2C are process timing charts showing the operation of the conventional TDMA voice information reading apparatus. In FIGS. 1 and 2A to 2C, the standards of a digital mobile telephone system to which the TCH read circuit in the TDMA voice information reading apparatus is applied are defined on the basis of xe2x80x9cRCR-27Dxe2x80x9d. In this system, a synchronization code word for synchronous detection is set in a reception slot, as shown in FIG. 2A.
The TCH data read window data S1 of high level is generated by the TCH data read window generation circuit 13 at a free-running timing as shown in FIG. 2B and input to one input terminal of the AND gate 12. The reception data S2 is input to the other input terminal of the AND gate 12 and the synchronous detection circuit 5. The synchronous detection circuit 5 detects the bit shift data S8 representing the shift of the reception data 52 from the prescribed timing and outputs the bit shift data S8 to the TCH data read window generation circuit 13.
When the synchronous detection circuit 5 detects the bit shift, an erroneous data portion in the reception data has already been output from the AND gate 12 to the DSP as TCH data or the voice output data S14. In this case, the DSP cannot perform normal voice data processing. As a result, the TCH data of the current slot cannot be processed as normal voice data although the synchronous timing of the next slot can be calculated from the bit shift data obtained from the current slot. Therefore, the channel quality degrades.
As described above, in the conventional TDMA voice information reading apparatus, TCH data of the current slot cannot be processed as normal voice data although the synchronous timing of the next slot can be calculated from the bit shift data obtained from the current slot. Therefore, the channel quality degrades to result in a low transmission efficiency and low reliability of data transmission.
The present invention has been made in consideration of the above situation of the prior art, and has as its object to provide a TDMA voice information reading apparatus which can normally output TCH data of a current slot as voice data even when data based on time division multiple access is received with a pull-out due to degradation in channel quality, thereby largely improving the transmission efficiency and reliability of transmission.
A TDMA voice information reading apparatus of the present invention comprises processing means for, in a pull-out of reception data based on time division multiple access, delaying the reception data pulling out synchronization and detecting synchronization before the reception data is read out, and then reading out voice data and outputting the voice data in order to normally read out and output the voice data.
In the TDMA voice information reading apparatus of the present invention, a delay time until the reception data is read out is a minimum time for synchronous detection.
In the present invention, phase matching of a read signal associated with a timing at which the voice data in the reception data is read out is adjusted by delaying the read signal or reception data in units of bits.
In order to achieve the above object, according to the first aspect of the present invention, there is provided a TDMA voice information reading apparatus comprising:
(a) a first shift register for storing, in units of bits, window data used to read out the voice data in the reception data, reading out the window data, and outputting the window data;
(b) a second shift register for storing reception data of a slot in units of bits and outputting the reception data with a timing shift of several bits before or after a synchronization code word stored in a reception slot on the basis of the reception data received at a prescribed timing;
(c) a synchronous detection circuit for comparing, in units of slots, a reception timing of the synchronization code word in the reception data with a free-running pulse internally generated at a prescribed timing and outputting bit shift data representing a phase shift of the timing;
(d) an AND gate for sending voice output data obtained by ANDing read window data phase-matching the voice data in the reception data and reception data delayed until establishment of synchronization, which is output from the second shift register;
(e) a selector for selecting the read window data and outputting the read window data phase-matching the voice data in the reception data on the basis of the bit shift data representing the position and the number of bits shifted from the prescribed timing, which is output from the synchronous detection circuit after reception of the synchronization code word in the slot; and
(f) a voice data read window generation circuit for generating the read window data at a free-running timing allowing reception of a synchronization code word in the next slot after reception of the synchronization code word in the preceding slot.
In order to achieve the above object, according to the second aspect of the present invention, there is provided a TDMA voice information reading apparatus comprising:
(a) a voice data read window generation circuit for generating read window data at a free-running timing allowing reception of a synchronization code word in the next slot after reception of a synchronization code word in a preceding slot;
(b) a first shift register for delaying the read window data from the voice data read window generation circuit in units of bits and outputting the read window data;
(c) a second shift register for storing reception data in units of bits and outputting delayed reception data;
(d) a synchronous detection circuit for comparing, in units of slots, a reception timing of the synchronization code word in the reception data with a free-running pulse internally generated at a prescribed timing and outputting bit shift data representing a phase shift of the timing;
(e) a selector for selecting the read window data from the second shift register, which is delayed by the second shift register, on the basis of the bit shift data representing the position and the number of bits shifted from the prescribed timing, which is output from the synchronous detection circuit after reception of the synchronization code word in the slot, and outputting the reception data; and
(f) an AND gate for sending voice output data obtained by ANDing read window data phase-matching the voice data in the reception data and reception data delayed until establishment of synchronization, which is output from the first shift register.
As is apparent from the above-described arrangements, the TDMA voice information reading apparatus of the present invention can output normal voice data from the current slot even when the reception data based on time division multiple access pulls out synchronization due to degradation in channel quality, so the transmission efficiency and reliability of transmission are largely improved.